1. Field of the Invention
This invention relates to the field of video recording and playback systems, and particularly to a method and apparatus for selectively omitting certain program content during playback of a recorded video signal.
2. Background Art
It is commonplace to record a commercial television program on a video tape recorder (VTR, also referred to as a video cassette recorder or VCR) for viewing at a later time. When later viewing the recorded program, many, if not most, viewers prefer to watch only the program material without also viewing commercials, promotional messages and the like that are typically broadcast at intervals during the program.
Numerous methods and devices have been proposed for automatically eliminating commercials and the like from a recorded program. For example, PCT Application No. WO081/00945 by Johnston and Koombes discloses a system for automatically detecting and editing commercial messages from a television broadcast signal. Their system detects the "breaks" in the television signal that characteristically occur prior to and at the end of a commercial message. Each such break triggers a timing circuit that has a timing interval slightly greater than the maximum expected duration of a commercial message. The timing circuit causes an associated VTR to switch from the "record" mode to the "pause" mode so that commercial messages will not be recorded. When the timing circuit times out without having been retriggered by further breaks. recording is resumed. Such a system is claimed to be relatively effective for eliminating commercial messages, but suffers certain drawbacks. In this regard, program material immediately following a commercial break is irretrievably lost since the VTR is held in the "pause" mode for a predetermined period of time (30 to 60 seconds or more) following each break in the television signal. Furthermore, additional program material may be irretrievably lost if the timing circuit is falsely triggered, such as by a fade between scenes in the program.
Other prior art systems have sought to overcome these drawbacks. For example, U.S. Pat. No. 5,151,788 to Blum discloses a system for eliminating commercials from a video signal that performs real time analysis of the video signal immediately following a blank frame. If there is a high level of "activity" in the signal immediately following a blank frame, a commercial message is presumed and the VCR is commanded to pause. On the other hand, if a low level of activity is detected, the preceding blank frame is presumed to be a fade and the VCR is commanded to resume recording. This approach solves the problem of losing a fixed amount of program material if a VCR pause if falsely triggered, but it is still susceptible to misclassification. If a program fade is immediately followed by an "active" scene, this will be misclassified as a commercial. On the other hand, a commercial with a low level of "activity" will be misclassified as program material.
Still other prior art systems detect the presence of a commercial after it has been aired and then rewind the VCR to continue recording at the beginning of the detected commercial. One such "reciprocating" system is disclosed in U.S. Pat. No. 4,750,052 issued to Poppy and Samelson. In this system, a pair of successive fades in the television signal separated by a time interval characteristic of a commercial will cause the VCR to be commanded to rewind to the point where the first fade was recorded. The VCR then continues recording, and the process will repeat if multiple commercials are broadcast back-to-back. This system permits an editing decision to be made after an entire commercial has been aired; however, as with the other systems previously described, program material is still irretrievably lost if there is a false detection of a commercial. Furthermore, the frequent rewinding of the tape during long commercial breaks accelerates the wear of the VCR tape transport mechanism as well as the tape itself.
All of the above described systems, and all other known prior art systems for selectively removing commercials from a taped television program attempt to remove the commercials during the recording process. Consequently, an error in the logic that identifies a portion of the television signal as a commercial will cause program material to be irretrievably lost. Furthermore, most such systems, even when false triggering does not occur, will lose some initial portion of a program immediately following a commercial break.